As shown in Patent Document 1, for example, an overhead crane that is installed in the ceiling of a factory or the like comprises a girder, which has a winder capable of lateral movement, spanning the distance between a pair of saddles that roll over parallel travel rails set up near the ceiling of the building. This winder can be an electric hoist that uses a cable as a winding support, an electric chain block that uses a load chain, or the like. Slinging equipment connected to a load is hung from a hook provided to a hook block suspended from the winder, and the load is moved by the overhead crane to the desired location.
Such overhead cranes are conventionally manipulated by successively pressing the six buttons (east, west, north, south, up, and down) on a wired remote apparatus hanging down from the winder, but when the load is large, there is the possibility that the load hanging from the winder will come into contact with the person manipulating the wired remote apparatus hanging down form the winder, which poses safety problems.
To solve this problem, remote apparatus that are operated wirelessly have been developed, such as the crane-use optical remote apparatus disclosed in Patent Document 2. This crane-use optical remote apparatus is more practical because it makes use of two or more light receptors that have wide-angle light receiving characteristics and are disposed under the winder main body, which deals with the problem that conventional wireless remote apparatus that makes use of radio waves tends to drive up the cost, and while costs can be easily reduced with an optical remote apparatus, if there is something that blocks light, the signals cannot be sent or received.
Patent Document 1: Japanese Patent Application Laid-Open No. 2004-75284
Patent Document 2: Japanese Patent Application Laid-Open No. H1 1-106179